As one of a press apparatus continuously pressing works sequentially a tandem pressing apparatus has been known. It includes a tandem pressing line in which plural tandem press are disposed, and a work conveying apparatus conveying works between adjacent tandem presses. The tandem press includes a bed, four uprights studded on the bed, a crown fixed at upper portions of the uprights, and a slide supported by the crown to be ascended and descended. To a bolster mounted on the bed a lower mold is set, while to the slide an upper mold is set.
For conveying the works between the adjacent tandem presses, a work conveying apparatus such as a conveying robot etc. has been used. FIGS. 7 and 8 show a work conveying apparatus for conventional tandem press disclosed in the Japanese Publication H6-47465. In this conventional art, a conveying robot 160, disposed between the first pressing machine 150 and the second pressing machine 155 disposed adjacent thereto, conveys the works from the first pressing machine 150 to the second pressing machine 155. A front/rear of the work is reversed during the conveyance thereof. Onto an arm 161 of the conveying robot 160 a vacuum cap 162 for conveying the work is mounted, while onto an upper mold 156 of the second pressing machine 155 a vacuum cap 158 for holding the work is mounted.
When the upper mold 151 ascends after completion of pressing by the first pressing machine 150, the arm 161 of the conveying robot 160 enters into the space between the upper mold 151 and the lower mold 152. Thus, the vacuum cup 162 for the work conveying absorbs the work W. The conveying robot 160 makes the work W to float up from the lower mold 152, and takes out the work from space between the first pressing machine 150 and the second pressing machine 160 at once, to reverse the front/rear thereof.
Then, being faced to space between the upper mold 156 and the lower mold 157 of the second pressing machine 155, the work W is pushed upwardly to be pressed onto the vacuum cap 158 for the work holding.
When the work W is absorbed to the vacuum cap 158, the vacuum cap 162 for the work conveying releases the work W, so that the conveying robot 160 is stood by at the area between the first pressing machine 150 and the second pressing machine 155. In this way, the work W having been pressed by the first pressing machine 150 is reversed the front/rear thereof, then supplied or fed to the upper mold of the second pressing machine 155.
In the above conventional art, the conveying robot 160 conveying the work W between the first pressing machine 150 and the second pressing machine 155 is disposed between the both pressing machines 150 and 155. As a result, a space 165 required for disposing the conveying robot 160 between the first and second pressing machines 155 makes a conveying distance (conveying pitch P) of the work longer.
Increase of the conveying pitch P makes a conveying time of the work W between the first and second pressing machines 150 and 155 longer, so that productivity of the pressed article decreases. The productivity can be somewhat improved by increasing the conveying speed of the work W, but absorbing ability by the vacuum cup 162 for the work conveying is apt to be shortened. Further, large drive source will be required for the high-speed conveyance.
The Japanese Patent Publication No. 2002-307116 has disclosed a conveying apparatus (transfer feeder) of a transfer press. As shown in FIGS. 9 and 10, the transfer press 170 includes a bed 171, four up-rights 173, a crown 175 and a slide 177. A lower mold is attached to a bolster 172 of the bed 171, while an upper mold is attached to the slide 177.
Spanning the adjacent transfer presses 170, a conveying apparatus 80 is disposed. It includes a pair of lifting beams 181 disposed along conveying direction of the work, servo motors 184 for ascending/descending the lifting beams 181, carriers 187 movably attached to the lifting beams 181, linear motors (not shown) for driving the carriers 187 in the conveying direction, and work holding means 194 having a cross bar 192 and a vacuum cap 193.
Proximity portions of the lifting beam 181 in the work conveying direction have length correspond to each of conveying areas T2, T3 and T4. The lifting beams 181 in the conveying areas T2 and T4 are positioned inside the lifting beam 181 in the conveying area T3. The servo motors 184 are supported on the uprights 171 by supporting members 185 to drive the lifting beams 181 upwardly and downwardly. The carriers 187 are attached to the linear motors, to be moved relative to the lifting beams 181.
The work W is conveyed by this conveying apparatus 180 in the following manner. In the conveying area T3, at the timing when the slide 177 having finished processing at the processing station W3 moves upwardly, the carrier 187 positioned at the predetermined height is moved to end of the processing station W3 along the lifting beam 181. With the vacuum cap 193 being positioned at center of the processing station W4, the lifting beam 181 descends to absorb the work W. Then, the lifting beam 187 ascends, the carrier 187 moves to end of the processing station W4, the vacuum cap 193 moves to a center of the processing station W4, and the lifting beam 181 descends to release the work W.
Next, the lifting beam 181 is ascended before the slide 177 of the processing station W4 fully descends. The carrier 187 is returned to substantial center of the conveying area T3 not to interfere with the slide 177 and the mold. Thereafter, after completion of the processing at the processing station W4, the lifting beam 181 and the carrier 187 are operated in the conveying area T4, in the same manner as that of the conveying apparatus in the conveying area T3.
This conveying apparatus 180 extending between the processing stations W2 and W3, and between the processing stations W3 and W4, is not for the tandem press but or the transfer press. In the transfer press having singe bed, whole of the processing station forms pair, so that an interval between the adjacent processing stations is short. Thus, there exits no space for disposing the conveying apparatus between the adjacent processing stations. For this reason, the conveying apparatus may be disposed over or spanning the adjacent processing stations.
In addition, the servo motor 184 driving the lifting beam 181 in the up-down direction consumes much power.
In the tandem pressing line, different from the transfer pressing line, one slide is provided for one bed in each of tandem presses, which means each tandem press is independent from remaining tandem presses. Accordingly, corresponding to increase/decrease of the numbers of articles, the tandem press can be added or removed. Also, even when the particular tandem press is broken, the article can be produced by the remaining normally operating tandem presses. Thus, it has flexibility in the article producing. However, the tandem press has disadvantages that the conveying distance longer than that of the transfer press decreases the producing ability.